Fix #29274: problem compiling cycles opencl kernel from directory with spaces.

Some drivers don't support passing include paths with spaces in them, nor does
the opencl spec specify anything about how to quote/escape such paths, so for
now we just resolved #includes ourselves. Alternative would have been to use c
preprocessor, but this also resolves all #ifdefs, which we do not want.

intern/cycles/util/util_path.h

@@ -46,6 +46,8 @@ void path_create_directories(const string& path);
 bool path_write_binary(const string& path, const vector<uint8_t>& binary);
 bool path_read_binary(const string& path, vector<uint8_t>& binary);
 
+string path_source_replace_includes(const string& source, const string& path);
+
 CCL_NAMESPACE_END
 
 #endif